The present invention relates to an improved hydraulic servovalve.
By way of background, hydraulic servovalves are well known. They generally include a torque motor and a valve assembly. The valve structure is located in a valve housing which conventionally has three bores therein. One bore is for the spool, a second bore is for the nozzle structure, and a third bore is for the filter. The fact that there are three bores in the valve housing produces certain inherent disadvantages. First of all, the valve housing has to be relatively large to accommodate the three bores and their associated structure. In addition, fluid conduits are required in the valve housing between all three bores, and this often requires complex machine operations and also sometimes requires a spool bushing, especially when the spool itself is of very small diameter in a high pressure system.
Filters cannot be eliminated when the fluid, such as aviation fuel, which passes through the valve, is relatively unclean so that it clogs the orifices of the nozzles. In addition, since aviation fuel systems for aircraft operate at a relatively low pressure, the spools have to be of relatively large size in order to be subjected to sufficiently large forces for moving them. The combination of a relatively large spool and the necessity for the separate filter bore, of conventional valves, causes the entire servovalve to be of relatively large size and weight which is undesirable, especially for aircraft fuel control applications.